In the Long Term Evolution (LTE) system, the random access technology is an important technology of the User Equipment (abbreviated as UE) access control in the communication system. The random access preamble of the LTE generally uses the ZC (Zadoff-Chu) sequence, and the random access preamble code is derived by selecting different cyclic shifts based on the ZC sequence. The random access subframe is made up of three parts, which respectively are a Cyclic Prefix (CP), a preamble sequence (Sequence) and a Guard Time (GT), as shown in FIG. 1.
The PRACH of the existing LTE system supports five kinds of random access preamble formats, which are Format0 to Format4, wherein, the Frequency Division Duplexing (FDD) supports format0 to format3, and the Time Division Duplexing (TDD) supports format0 to format 4; different random access preamble formats correspond to different CP lengths (TCP), Sequence lengths (or, the number of sampling points of the preamble sequence, abbreviate as TSEQ) and the GT lengths (or, the number of sampling points of the guard interval, abbreviated as TGT). The types of the random access preamble format supported by the TDD mode in the LTE system at present, and the TCP, the TSEQ and the TGT corresponding to every format are shown in Table 1.
TABLE 1random accesspreamble formatTCPTSEQTGTFormat 03168Ts 24576Ts2976TsFormat 121024Ts  24576Ts15840Ts Format 26240Ts2*24576Ts6048TsFormat 321024Ts 2*24576Ts21984Ts Format 4 448Ts  4096Ts 614Ts
In the random access preamble format shown in Table 1, Format 0 to Format 3 are transmitted in the normal uplink subframe, the length of the ZC sequence (NZC) is 839, the Format 4 is transmitted in the UpPTS, and the NZC is 139.
In the current LTE system, the values of the cyclic shift quantities (NCS) under every random access preamble format are configured; by taking Format 0 to Format 3 as examples, the cyclic shift quantity (NCS) set is configured, divided into a restricted set and an unrestricted set; as to Format 0 to Format 3, the values of the NCS are shown in Table 2, wherein, 0 in the unrestricted set represents 839.
TABLE 2NCSNCS valueconfigurationUnrestricted setRestricted set00151131821522318264223252638632467385584668959821076100119312812119158131672021427923715419—
In the current LTE system, in order to withstand the frequency offset generated by the high-speed movement of the terminal, the cyclic shift restriction is used, that is, when the terminal is in a high-speed mobile environment, only the NCS values in the restricted set in Table 2 are allowed to use. While the NCS values in the restricted set are generally smaller, the greatest is only 237, and such a NCS value determines a smaller cell coverage radius. So, the current random access technology cannot satisfy the requirement of the high-speed movement of the terminal and the larger cell coverage radial simultaneously.